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Anaerobic Digestion & Fermentation
Equipment and Research
OPERATING
MANUAL Batch/ Fermenter Range
(Nautilus, Pegasus, Phoenix models)
Anaero Technology Ltd. Unit 5, Ronald Rolph, Wadloes road, Cambridge, CB5 8PX
Email: [email protected] / [email protected] / [email protected]
Phone: (+44) 01223778210 / (+44) 07397555544
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TABLE OF CONTENTS
1. Introduction ......................................................................................................................... 3
2. Equipment Overview ........................................................................................................... 4
2.1 Reactor module ............................................................................................................ 4
2.2 Mixing module ............................................................................................................. 5
2.3 Gasflowmeter module ................................................................................................. 5
2.4 Arduino Datalogger ..................................................................................................... 6
3. Operation principles: Setting up of a BMP test .................................................................. 7
3.1 Preparation of the gasflowmeter ............................................................................... 7
3.2 Preparation of the water bath .................................................................................... 9
4. How to start your test and prepare your samples ........................................................... 10
4.1 Pre-analysis .................................................................................................................. 10
4.2 BMP analysis and Calculations: Calculating the amount of sample and inoculum ................ 10
4.3 Setting up Arduino Datalogger .................................................................................... 17
- Data logger use .......................................................................................................... 17
- Biogas production curve ............................................................................................ 22
- Other utilites .............................................................................................................. 25
5. Suggested Reading: BMP production curves and limitations (Inhibition and toxicity) .. 26
6. Frecuently questions ......................................................................................................... 28
7. Routine Checks .................................................................................................................. 30
8. Spares................................................................................................................................. 30
References ................................................................................................................................ 30
LIST OF ACRONYMS
BMP Biomethane Potential STP Standard conditions for Temperature and Pressure
AD Anaerobic Digestion VAC Volts of Alternating Current
CSTR Continuous Stirred-Tank Reactor VDC Volts of Direct Current
HDPE High-Density Polyethylene VFA Volatile Fatty Acids
3
BMP MANUAL
1. INTRODUCTION
2. Biomethane Potential (BMP)1 is a biological test to evaluate the
potential methane/biogas volume generated from a material
(substrate). The test comprises two elements: a) Inoculum and b)
sample. Inoculum (seed) is fed an amount of sample on a VS ratio
basis (M/F), gas yield production is then measured continuously in
real time. The gas is measured and converted to units of ml
gas/gram VS substrate at Standard conditions for Temperature and
Pressure (STP).
The BMP test subtracts the biogas yield of inoculum from that of
reactors containing sample + inoculum. For this inoculum, only reactors are used to determine the
baseline yield of inoculum on ml/g VS inoc., which improves the consistency of the test. Through a
gearbox, Anaero BMP equipment uses one single motor to mix 15x1-litre reactors, assuring equal mixing
intensity2 for all. By immersion in a water bath with a tight water lid, temperature is maintained constant
for all reactors and bath water evaporation minimised even when operating in thermophilic mode. The
control of the mixing and temperature minimises operational differences between reactors, improving
the consistency of the results. Moreover, Anaero BMP operates at low gas head pressure to reflect low
pressure operating conditions in most Continuous Stirred-Tank Reactor (CSTR) digesters. The equipment
has a built-in battery backup for the gas flow meter (up to 15h) to avoid data loss during power outage.
The Anaero Technology BMP sets optimise technical performance in the following areas:
➢ Larger reactor volume. 1-Litre reactors allow larger sample use, easier to handle and smaller errors
(more gas generated in bigger reactors = less error from missed gas bubbles). However, it is also
possible to operate with smaller test volumes in the bottle (from 350ml to 900ml).
➢ Mixing consistency. All reactors are mixed at exactly the same speed through stainless/silicone paddles
driven by a gearbox (1 motor for 15 reactors). Consistent mixing even for high % Dry Solids (DS).
➢ Real time gas flow measurement with automatic conversion to standard temperature and pressure
and protection of data with built-in power back-up for gas flow meter.
➢ Low bath water evaporation loss. Standard water bath with tight-fitting cover that minimises bath
water evaporation loss even when operating at thermophilic temperature.
➢ Access to reactors during test. Gas-tight access ports to interior of digesters without affecting gas
monitoring (measure pH, redox, VFA, or supplement during test without opening reactors).
➢ Ease of calibration. Use a simple syringe to confirm the consistency of flow measurements.
➢ Flexible addition of bespoke ports. Large diameter cap allows fitting of additional ports as required by
your protocol, as septum or larger probes (*small additional cost for extra ports).
1 In the UK, residual biogas potential (RBP) is an equivalent test. It is described in WRAP report OFW004-005 and it has become a certified method. 2 Variations in mixing speed between reactors in a set can impact the kinetics of biogas production.
Figure 1. Standard BMP/RBP set.
4
Figure 2. Reactor module
3. EQUIPMENT OVERVIEW
Table 1.BMP equipment features.
Reactors per set 15
Reactor volume (L) 1 Materials High-density polyethylene3 (HDPE) (reactors), 316 Stainless steel4 (mixers),
polycarbonate5 (gas flow meter) and silicone (blades). Hight temperature tolerance. Mixer motors per set 1 Power 110 or 220VAC for bath. 6VDC backup incl. for gas flow meter; 24 VDC mixer motor. Measurement resolution (ml)
7 – 10
Measurement method Volumetric displacement with real-time temperature and pressure sensors for STP. Software Arduino with automatic conversions and calculation, open source. Dimensions W570mm X D340mm x H 700mm (reactor set); W1000mm X D200mm x H200mm (gas
flow meter). Country of origin United Kingdom.
3.1 REACTOR MODULE
1) 1-litre HDPE reactor bottles
2) Reactor heads
3) Water bath
4) Bath lid
5) Access port
6) Gas outlet
7) Reactor mixer paddle
Description:
- Bioreactors: 1-litre wide mouth HDPE bottles with easy handling, allow larger samples and inoculums to
be processed, which further reduces potential errors. Stainlees steel/silicone paddles deliver consitent
and continuous mixing to all digesters in each and respond to the higher resistance when samples with
high solids are tested. HPDE is biologicaly innert and remains stable at 100°C. Most commercially-available
BMP sets do not guarantee equal mixing for all reactors in the set. Some rely on daily manual shaking,
shaking surfaces, magnetic stirrers, etc., which is ok for absolute values of BMP but limits the use of kinetic
data for rapid evaluation of inhibition or of the effect of feedstock composition on dynamics of biogas
production.
- Water bath. The reactors temperature of operation is controlled by immersion of reactors in a water
bath. A lid that holds the reactors in place has been designed to minimise the loss of bath water by
evaporation, facilitating tests at thermophilic temperatures without the common issues of water
evaporation when operating at those conditions.
3 Reference for material tolerance: British plastic federation (2017). ‘Polyethylene (High Density) HDPE’ http://www.bpf.co.uk/plastipedia/polymers/hdpe.aspx 4 Reference for material tolerance: British Stainless Steel Association (2001). ‘Structural Design of Stainless Steel’. http://www.bssa.org.uk/cms/File/SCI%20291%20Structural%20Design%20of%20Stainless%20Steel.pdf 5 Reference for material tolerance: British plastic federation (2017). ‘Polycarbonate PC’ http://www.bpf.co.uk/plastipedia/polymers/polycarbonate.aspx
5 4
2
3
7
1
6
5
Figure 4. Gas flow meter buckets (top) and Gas flow meter module (bottom).
3.2 MIXING MODULE 8) Mixer drive box 9) Motor
10) Mixer module support posts
Description: All reactors are mixed at exactly the same speed and using stainless steel/silicone paddle systems that guarantee even mixing, even for high solids mixtures (e.g. 12%DS). At higher solids, it is needed to check if the motor is not over loaded and fit rods to avoid reactor spinning.
3.3 GAS FLOW METER MODULE 11) Gas flow meter block 12) Tumbler bucket
13) Temperature sensor
Description: Gas generation is measured using a liquid displacement gas flow meter. The gas flow meter
is a single Perspex block with 15- 0.2l cells and Perspex tumbling buckets of around 7ml gas volume. A
spare cell (cell 16) is used for automatic monitoring of temperature. A barometer in the Arduino logger
continuously monitors atmospheric pressure for STP correction. The liquid in all cells is interconnected to
keep them at exactly the same head, for equal head pressure in all reactors (liquid specifications: Table
2). Each cell has a tumbling bucket with active volume of around 7ml (easily calibrated by user- See section
3.1). The smaller measuring volume allows for better recording of the kinetics of the test, especially after
the initial phase of high gas production. However, the smaller the measurement volume, the larger the
potential error from uncounted gas bubbles. To minimise potential error during gas measurement a
minimum counting volume of 5ml has been designed and attention has been paid to the size of gas
bubbles entering the measuring vessel. The diameter of the nozzle orifice where gas enters the
measurement cell is machined to 1.5mm, reducing the size of gas bubbles and minimising the potential
impact of uncounted odd bubbles by-passing the tumbling bucket.
Figure 3. Mixing module and reactor module.
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12
13
11
9
10
6
Some requirements for the use of the Gas flow meter:
➢ Avoid sagging in gas lines which can accumulate condensation and increase head pressure in
reactors affected.
➢ Avoid connecting only a few gas bags (to collect gas samples) in the Gas flow meter. If it is
possible, connect all cells to gas bags to avoid pressure differentials between cells.
➢ Ideally, the gas flow meter should be placed lower than reactors.
➢ Avoid kinks in gas lines.
➢ Rapid cooling of water bath can create vacuum which sucks water from the gas flow meter
into reactors and loose data.
The liquid inside the Gas flow meter can be an acidified or distilled water (for total biogas), or caustic solution (for CH4-only). Different possibilities are detailed bellow.
Table 2. Gas flow meter liquid.
Liquid on the Gas flow meter pH or molar concentration Parameter measured H2O - CH4, CO2, H2S, etc.
Na(OH) + H2O - CH4 only HCl + H2O pH=2 6 CH4. CO2, H2S
3.4 ARDUINO DATALOGER
The IT system consists of an Arduino 2560 Mega microcontroller which acts as the main controller
for the data logger. Connected to this is a specially designed ‘latch shield’ consisting of 15 separate
Set/Reset latches. When one of the tumblers in the gas flow meter tips, a magnet attached to the
tumbler causes a reed switch to close, and the latch associated with that channel locks to store the
occurrence, time, temperature and pressure. Each tumbler event is captured in hardware by the latch
shield, guarantying that all tumble events are registered.
6 Reference:Walker, M. et al. (2010). ‘Residual biogas potential test’. Bioresource Technology. 100(24) 6339-6346. http://www.wrap.org.uk/sites/files/wrap/Residual%20Biogas%20Potential.pdf
Figure 5. Gas flow meter module sketch.
Operational position
of drain port
Position at calibration (with
all buckets empty of gas!)
Arduino
Datalogger
Do not let gas bags fill
Ensure valve is not left shut! (if
you do, you will lose the test)
7
Figure 6. Gas flow meter, hose position detailed.
4. OPERATION PRINCIPLES: SETTING UP OF A BMP TEST
4.1 PREPARATION OF THE GAS FLOW METER
1. Pass the hose provided through the holes in the lid of the gas flow meter and connect firmly to
the gas inlet at the bottom.
2. Fill the gas flow meters (see table 2) until liquid drops from the spill point.
3. Calibrate the gas flow meters: To obtain accurate results it is needed to level the gas flow meter
(it could done using a spirit level).
3.1 Level the gas flow meter.
3.2 Ensure that all buckets are empty of gas.
3.3 Change the position of drain port to up position.
3.4 Fit calibration syringe to gas line and gently
introduce air to cause one tumble (dummy tumble)
and do 3 tumbles each way (1 dummy tumble + 6
tumbles in total).
Do not keep pressing the calibration syringe when
the tumbler is tipping as you will cause more
bubbles, increasing the error.
3.3
You can fill the buckets
fast at the beginning and
slow down just before
tumbler starts tipping.
Figure 8. (3.1) Gas flow meter levelled, (3.2) Operational position of the drain pipe, (3.4) Gas flow meter calibration.
Figure 7. How to fill the gas flow meter.
3.1
3.4
8
3.5 Record the millilitres per tumble of each bucket associate to each reactor. This value is
the quantity of biogas that each bucket will measure per tumble.
For this purpose, next steps explain one of the possible methods to follow.
3.6 Write in a paper sheet or in your computer a table with the first column and first file,
as the ones showed in the Figure 9.
3.7 Introduce air with the syringe into the bucket until the first tumble happens. The first
tumble is a dummy tumble to take out the air from the bucket. Once the dummy tumble is
made take the reading on the syringe as your Start point and continue introducing air to
make the 6 tumbles (3 each way). Make note of the end reading after 6 tumbles on the
syringe and calculate the ml/tumble by dividing the distance travelled by the syringe to
make the six tumbles by no of tumbles (6) as shown below
3.8 To calculate the millilitres per tumble use the formula showed below:
𝑚𝑙
𝑡𝑢𝑚𝑏𝑙𝑒=
(𝑆𝑡𝑎𝑟𝑡 𝑝𝑜𝑖𝑛𝑡 − 𝐸𝑛𝑑 𝑝𝑜𝑖𝑛𝑡)
𝑁º 𝑜𝑓 𝑡𝑢𝑚𝑏𝑙𝑒𝑠𝑜𝑟
(𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑡𝑟𝑎𝑣𝑒𝑙𝑙𝑒𝑑 𝑏𝑦 𝑡ℎ𝑒 𝑠𝑦𝑟𝑖𝑛𝑔𝑒(𝑚𝑙))
𝑁º 𝑜𝑓 𝑡𝑢𝑚𝑏𝑙𝑒𝑠
𝐸𝑥𝑎𝑚𝑝𝑙𝑒 𝑅𝑒𝑎𝑐𝑡𝑜𝑟 𝑁º1 𝑚𝑙
𝑡𝑢𝑚𝑏𝑙𝑒=
(56 − 17.5)
6= 6.41
𝑚𝑙
𝑡𝑢𝑚𝑏𝑙𝑒
3.9 Once complete, the calibration values (ml/tumble) from the table can be entered in the
set-up file of the Arduino software installed on your laptop (See section 3 to see the
operational principles of the BMP and section 4.3 where Arduino set up is explained in
detail).
Figure 9. Gas flow meter calibration sample sheet.
Reactor Nº
Start point ml
End point ml
Nº of tumbles
ml/tumble
1 56 17.5 6 6.41
2 57 17.5 6 6.58
3 57 18 6 6.50
4 56 17 6 6.50
5 56 17.5 6 6.41
6 57 17.8 6 6.53
7 57.5 17 6 6.66
8 56 17 6 6.50
9 57 17.5 6 6.53
10 57 18 6 6.50
11 57 17.5 6 6.58
12 56 17 6 6.50
13 57.5 17 6 6.66
14 57 18 6 6.50
15 56 17 6 6.50
Gas flow meter calibration Date: 07/12/17
sample sheet
9
3.2 PREPARATION OF THE WATER BATH
Before setting up the water bath, it would be necessary to prepare the samples (See section number
4).
a) Once the samples are prepared, fit the reactor heads and place all the reactor bottles in water
bath.
b) Place the bath lid. Flush the reactor bottles and the gas flow meter with selected gas as required
and ensure all the tumblers in the gas flow meter are in the down position.
c) Fill water in the water bath and set it to the required temperature (maximum temperature 95º).
d) Connect all the reactor bottles to the other end of the hose coming out the gas flow meter.
e) Place the mixing gear box on top of reactor bottle heads.
f) Connect the motor to the power supply.
Figure 11. Complete Water bath with reactors and bath lid.
Figure 10. Water bath with reactors.
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4. HOW TO START YOUR TEST AND PREPARE YOUR SAMPLES
4.1 PRE-ANALYSIS
➢ Total Solids (TS):
Total solid is the dry matter of a sample after the moisture has
been completely removed.
To measure TS, crucibles can be used to test multiple samples
(see picture 3). Weigh the empty crucibles (C) g using a weighing
scale, weigh the crucibles again with fresh feedstock samples
(C+S1)g . Dry the samples in an oven at 105ºC for 24 hours. After
24 hours take the crucibles out, cool and then weigh them again
(C+S2) to determine the dry solids. The same crucibles after
weighing for dry solids can be used to determine the volatile
solids (VS).
➢ Volatile Solids (VS):
Volatile Solid is the organic dry matter of a sample. To carry out the analysis of VS, place the
crucibles with the dried samples, obtained previously, in the oven at 550ºC for 4-5 hours. After 4-
5 hours, the crucibles with ash left are cooled and weighed again (C+S3).
4.2 BMP ANALYSIS AND CALCULATIONS: CALCULATING THE AMOUNT OF SAMPLE AND INOCULUM
Measurements of TS and VS are required to know how much sample you need to use on the BMP
test. An spreadsheet with all the calculations will be provided with the BMP test.
1. Firstly, complete the spreadsheet (tab: TS VS) provided with the measurements done for TS and
VS7.
o C: Weight empty crucibles.
o C+S1: Crucibles with the samples.
o C+S2: Weight of the dry crucible and dry solids after oven.
o C+S3: Weight of the crucible and dry solids after furnace.
2. Calculate the weight of the samples without the crucible weight: (this will be automatically
calculated by the spreadsheet).
7 It is needed to write the values in red columns, black and white ones will be automatically calculated by the spreadsheet.
Figure 12. Crucibles with samples before and after Total solids and volatile solid analysis.
Wet sample
S1=(C+S1)-C
Dried solids
S2=(C+S2)-C
Ash
S3=(C+S3)-C
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3. Calculations of: volatile solids (dried solids – ash), dried solids % of wet weight, volatile solid
% of wet weight, volatile solids % of dried solids (wet weight).
4. Calculations of: DS % wet weight average, VS % wet weight
average, VS % DS wet weight average.
..
5. Open the second tab (Set-up calcs). The Inoculum VS (%w/w) value will appear at the top
of the tab.
6. Give to each reactor a sample description in the spreadsheet, in order to easily recognise
which samples are in the different reactors. To differentiate them while you are conducting
the BMP analysis, it is necessary to allocate numbers to each reactor (See figure12).
Volatile solids
VS=S2-S3
DS % wet weight
DS%w
w=
S2
S1X100
VS % wet weight
VS%w
w=
S2 − S3
S1X100
VS % DS wet weight
VS%DSw
w=
S2 − S3
S2X100
EXAMPLES:
Average DS % wet weight
DS%w
w=
J3 + J4 + J5
3
Average VS % wet weight
VS%w
w=
K3 + K4 + K5
3
Average VS % DS wet weight
VS%DSw
w=
L3 + L4 + L5
3
12
7. Weigh the empty 1-litre HDPE bottles using a weighing scale and allocate numbers to each
reactor.
8. Fill all the 15 1-litre bottles with ‘X’ grams of inoculum (Target weigh of inoculum = 650g) and
weigh again (actual weight). Put the value of the actual weight value in the Set-up calcs tab (e.g
650.3g). The spreadsheet will automatically calculate the grams of VS Inoculum mass.
9. Set up a ratio8 of Substrate: Inoculum (e.g. 1:4). Do not exceed 1g Sample:10g Inoculum (See
reference 1 to understand how set up a ratio).
8 Black and white values are automatically calculated by the spreadsheet. Red ones have to be manually written.
EXAMPLES:
Inoculum mass VS:
Inoc. mass VS = Inoculum VS (%w
w) 𝑥
Actual Weight of inoc.(g)
100= 6.00 𝑥
650.3
100= 39 g
Ratio Substrate:Inoculum 1:4
Figure 13. Reactors number allocation.
Figure 14. Inoculum disposed in HDPE bottles.
13
10. Based on the ratio of grams of VS of inoculum to grams to VS of substrate used, it is calculated
the amount of feedstock to be added in the 15 1-litre reactor bottles (for example, for a ratio of
4g of VS of inoculum to 1 g of VS of substrate in digestate analysis you will need Inoculum mass
VS ÷4 g VS as sample).
11. Pour into respective reactors the quantity of sample already calculated (‘Target weight of sample
(g) to achieve the ratio fixed’) in the spreadsheet, weight them and write the value in ‘Actual
sample weight (g) added to the reactors’ column.
12. The spreadsheet will automatically calculate the amount of sample mass in terms of VS.
EXAMPLES:
Target sample VS (g) to achieve the ratio fixed:
Target sample VS (g) =Inoculum mass (g)
Subsdtrate: Inoculum=
39
4= 9.76
Sample VS (%w/w): Calculated in the previous tab (TS VS).
Target weight of sample (g) to achieve the ratio fixed:
Target sample VS (g) =Target smaple VS (g)x100
Sample VS (%ww
)=
9.76 ∗ 100
14.59= 66.87
Figure 15. Inoculum and sample disposed in HDPE .bottles.
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13. Finally fit the reactor heads and place all the reactor bottles in water bath (follow the instructions
given in the Section 3.3).
The total amount of biogas produced by the material will be calculated by the gas flow meter. The gas
produced by the material can be calculated as it is showed below. The amount of biogas produced by the
material can be a negative value, caused by an inhibition/toxicity problem (See section 5: Suggested
reading to know more about inhibition and toxicity):
‘Y’ grams of sample
‘X’ grams of inoculum
Total Gas produced by (X+Y) = a
Total Gas produced by X = b
Total Gas produced by Y (Sample) = a-b
Total= (X+Y) grams
Example 2:
Total Gas produced by (X+Y) = 250 L Kg VS-1
Total Gas produced by X = 200 L Kg VS-1
Total Gas produced by Y (Sample) = 250 – 200= 50 L
Kg VS-1
EXAMPLES:
Sample mass VS:
Sample mass VS (g) =Inoculum mass (g)
100=
66.89 x 14.59
100= 9.759
Example 3:
Total Gas produced by (X+Y) = 200 L Kg VS-1
Total Gas produced by X = 250 L Kg VS-1
Total Gas produced by Y (Sample) = 200 – 250= - 50 L
Kg V S-1 NEGATIVE VALUE (See section 5)
15
Example 4:
SAMPLE: As an example, we will suppose that we need to measure the biomethane potential of a sample of food waste.
We will presume that we have a 20g sample of food waste with 10%VS of wet weight. Therefore, we have 2g of volatile
solids (VS) as sample, assumed to be mainly organic degradable material.
Since we want to evaluate how much biogas would a digester produce when fed this material, we use anaerobic digestate
as inoculum (seed) for the test.
It has been established that in order to not shock the inoculum with too much sample and to be able to make use of the
kinetics of biogas production, a volatile solids (VS) ratio Inoculum: Sample between 4:1 and <10:1 is recommended to
minimise potential organic shock to the inoculum as the test is set. In this example we will use a 5:1 ratio.
INOCULUM: The inoculum is 2.5% VS of wet weight (means that for one kilo of liquid inoculum we have 25g of volatiles
solids, assumed to be mainly anaerobic bacteria). We have 400g of sample at 2.5%VS of wet weight. This means that we
have total 10g VS as anaerobic inoculum.
MEASURING THE POTENTIAL BIOGAS YIELD OF A SAMPLE: To carry out the test, first we need to measure how much
biogas is produced by the inoculum alone (litre of biogas per kg of VS). This is done preparing three digesters containing
inoculum alone and measuring the biogas produce over a period of 30 days, or as long as the test lasts.
We subtract the biogas produced by the inoculum in the test from the “inoculum plus sample reactors”. This subtraction
gives us the biogas potential of the sample, we then convert it to litres of biogas per kg of VS.
We measure each sample or inoculum in triplicates to have consistent results. This is because this is a biological test,
susceptible to unpredicted variability, and samples can be blends of different compounds with potential for bias, for
example if lumps of sample are present. Never do a test using only one control reactor!
Sample (2gVS)
Food waste
Inoculum
(10g VS)
Inoculum
(10g VS)
Inoculum
(10g VS)
1001ml biogas 1005 ml biogas 1020 ml biogas
From the above results would have the
following yields for the inoculum:
1001ml/10gVS
1020ml/gVS 100.1, 102, 100.5
1005ml/gVS
Average inoculum yield =
(100.1 + 102 +100.5)/3 = 100.86 ml
biogas/ g VS inoculum
(or litres biogas /kg VS)
16
Therefore, the sample present in each of the reactors above would have produced:
2300ml gas total - 1008.6ml biogas from inoculum = 1291.4 ml biogas/2 g sample: 638.2ml/gVS
2250ml gas total - 1008.6 ml biogas from inoculum = 1241.1 ml biogas/2 g sample: 620.5ml/gVS
2285ml gas total - 1008.6 ml biogas from inoculum = 1276.4 ml biogas/2 g sample: 638.2ml/gVS
Thus, the average Biogas potential for the sample is: (638.2+620.5+638.2)/3 = 632.3ml/g VS
(This calculation is done on a daily basis and results in the cumulative graphs, a sample will normally
produce more biogas per gram).
If the sample used produces biogas, there will be a positive value when the gas from the inoculum is
subtracted. This will be reflected on an upward yield graph.
However, when inhibition or toxicity occur, subtracting the biogas produced by the inoculum from
the sample reactor would give a negative value reflected on a downward trend in the biogas yield
(See section 5).
Examp
Inoculum
(10g VS)
Inoculum
(10g VS)
Since we know the average biogas yield of
the inoculum per gram VS is 100.86ml/gVS
inoculum, and we have 10g VS of inoculum
in each of the samples, each of the reactors
above containing sample would have
1008.6ml of biogas corresponding to the
inoculum with which the sample was
seeded (area in grey).
17
4.3 SETTING UP ARDUINO DATALOGGER
A BMP280 barometric pressure, a microSD card reader and a
thermocouple amplifier are connected to the Arduino. All tumbler
events are written to a log file on the microSD card including the
channel number, the time at which the event occurred, the air
pressure at that time and the temperature as recorded by the
thermocouple. For ease of use, other log files (e.g. a summary of what
has happened in the last 24 hours) which are calculated from this event
data, are also stored on the memory card. A suite of Python utilities
has also been developed to simplify set up and operation of the data
logger.
Data logger use
a) A master folder of Arduino software will be provided by Anaero with two versions of software
(software that runs on a 32 bit operating system and software suitable for 64 bit operating
system). Check the properties of your computer’s processor (also called a CPU) and see if it is
32-bit or 64-bit9.
b) Depending on your computer properties copy the right version of Arduino software (64 bit
folder or the 32 bit) from the Master software folder provided and paste it on your desktop. Rename the folder copied : right click on the folder, select copy, right click on the desktop and select paste then right click on the new folder, select Rename and rename the folder to relevant name (e.g.: Gas_Flow_1 or Gas_Flow_2).
c) Open the folder10 you have just created (it should contain the four Python utilities (filegrab,
fastgrab, monitor and startrun) in the form of .exe files, along with a template for the setup.csv
file.
d) Open the setup file in Excel format (normally the computer will open the folder via Excel by default). The setup file will be displayed in the style of a spreadsheet. The setup file allows a sample name to be associated with each of the 15 channels, specifies which channels are being used and named them, which channels are ‘inoculum only’, the mass of inoculum volatile solids
9 Open the main menu of your computer, press ‘your computer’, click right on ‘C:’, go to properties and check type of system (32 or 64-bit). 10 If you are running more than one system you will need a different folder for each system, each of which should contain the relevant setup.csv and the three .exe files.
Figure 16. Arduino datalogger.
Figure 17. Contents of Arduino folder.
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for each channel and the mass of sample volatile solids for each channel (inoculum only channels will, by definition have a zero entry for their mass of sample volatile solids). The final column contains the calibrated tumbler volume for each channel.
e) Calibrate the gas flow meter and keep the values ready to be entered into the set-up file (See section 2.3 where the calibration of the gas flow meter is explained).
f) Edit the contents of the spreadsheet to match your system/experiment: Insert the ml/ tumble
values (Section 2.3) obtained during the gas flow meter calibration (Column Figure 18). Insert the Inoculum VS mass (g) and sample VS mass (g) , already calculated in the calculation sheet provided (Section 4.1 and 4.2 – Coloumn E and Coloumn K in sample spreadsheet highlighted in yellow).
g) Save the Excel spreadsheet, clicking on File -> Save. This brings up a prompt to check that you
wish to save the file in .csv format. Click on “Use TEXT CSV Format”. Close the Excel
spreadsheet.
h) Once the setup.csv file has been generated by editing the template provided, it can be
transferred to the Arduino11 and the run started using the ‘startrun’ utility. Make sure the gas flow system is powered using the power supply provided (Figure 19 1 to 2) and the gas flow meter is connected to the laptop using the USB cable (3 to 4) then double click on the startrun icon in the folder created at Step 1.
11 When connecting a computer to the Arduino, always disconnect and reconnect the computer from the Arduino end (i.e. the square shaped ‘type B’ USB plug), not by unplugging or connecting the USB lead from computer using the rectangular ‘type A’ plug. If you unplug or reconnect at the computer end, there is a risk that a spike over the USB connection as you make the connection can cause the Arduino to reset – this is much less likely if the connection is made/broken using the USB ‘type B’ plug/socket at the Arduino end.
Figure 18. Data CSV format setup spreadsheet file.
1
Figure 19. Arduino connexions. The numbers show the connection procedure order to be followed.
3
4
2
1
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g) Make sure that the ON/OFF Arduino button is in ON mode
(See Figure 20).
h) Startrun utility initialises the logging system and transfers
the data from the setup.csv file over to the system. The system will ask which port of the computer you will use (called COM + a number). In the case of the example Figure 21, the name of the port is COM10 (the system will tell you which port are you using), simply write COM10 and press enter12.
i) Arduino will ask if you want to copy or deleted old data. Directly press ‘D’ and ‘enter’ to delete
you data or copy it and then delete it (See figure 22).
j) Once the files have been copied or deleted, the system will complete its self-test routines and
prepare to transfer the data in the setup.csv file.
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12 If there is any problem with Arduino COM connection to the laptop, try to change the wire to another computer port.
Figure 20. Arduino connections details.
ON
Figure 21. Arduino startrun.
Figure 22. Arduino startrun 2.
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k) Pressing ‘enter’ again to starts the transfer process (once this has completed, the data which
has been stored by the logging system is written back to the console and also to the setup.csv
file). The data logger does perform range checks on the data received and will display warnings
if unexpected or out of range entries are found. It is important to check that the data written
back match what was send. This can be done by examining the information displayed on the
console or by opening the setup.csv file in Libre Office. You will see that the data written back
from the data logger are appended to the file.
Figure 23. Arduino startrun 3.
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Figure 24. Arduino transfer process.
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l) Make sure that laptop-Arduino and Arduino-Power supply are connected. Also, at this stage all
the reactors are placed in the waterbath and all the gas hoses are connected from the reactors
to the gas flow meter. To start the gas flow log, press ‘enter’ – the system is now live and
recording all tumbler tips. When a tumbler tip is detected an update is sent to the console. In
between tumbler events, the time stamp on the console is updated every 10 seconds. To leave
the startrun program press any key on the keyboard. It can take the utility a short while to tidy
up and close down.
m) Arduino will collect the gas production, which could be downloaded in your laptop.
Biogas production curve
n) Plotting Pivot chart: Copy daily.csv to the desktop so the original remains in the test directory
and then double click on the daily.csv file that is on the desktop to open it.
o) Delete the first row ('file uploaded 2017-11-28…'), and the last one (that says 'writeback
completed 2017-11-28…').
p) Now highlight all the data you wish to graph (whole table) and select Pivot Chart and click on OK.
Figure 26. Creating a Pivot Chart 1.
Figure 25. Excel file with the values downloaded from Arduino.
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q) A new tab will be created with the Pivot Chart, as it is showed the figure 27.
r) Select the Pivot Chart Fields and drag that fields to the areas below (see figure 28).
Areas Pivot Chart Fields
• LEGEND: Channel number
• AXIS: Days
• VALUES: Sums of Cumulative net volume.
Figure 27. Creating a Pivot Chart 2.
Figure 28. Creating a Pivot Chart 3.
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s) Move the Chart to a new tab (see figure 29) and change the chart type to: Line Chart (see figure 30).
Figure 30. Creating a Pivot Chart 5.
Figure 32. Creating a Pivot Chart 6 (Change to Line Chart).
Figure 29. Creating a Pivot Chart 4.
Figure 311. Creating a Pivot Chart 6.
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t) Finally you obtain a graphic showing the cumulative biogas production curve of each sample, produced during the BMP test.
Other utilities
• Filegrab: implements transfer of ALL data recorded by the logging system to the laptop. This
comprises the event log, a cumulative and incremental hourly report, a cumulative and
incremental daily report and a cumulative four hourly snapshot. After a run of several days several
thousand lined of data are produced so it can take a while for all data to be transferred. The utility
closes itself a short time after all data have been transferred. The name of each file written on the
laptop includes a time and date so is unique; as such the utility can be run as many times as
required without having to remove any files from the folder
• Fastgrab: performs the same function as filegrab but only transfers the event log and the daily
summary so takes much less time to complete. The utility closes itself a short time after all data
have been transferred. As with filegrab, the file names include a time and date so previous
transfers are not over-written.
• Monitor: allows live observation of the system but doesn’t transfer any data.
Note that when connecting to a ‘live’ gas flow meter mid-run, in order to minimise the possibility of a
short circuit or spike disrupting things, always power up the laptop unattached, then plug the USB lead
into the laptop and then connect the USB lead from the laptop to the flying lead coming off the gas flow
meter. If the USB lead is connected in the reverse order there is a risk that as the lead is plugged into the
laptop a short or power spike is generated which could affect the data logger.
Figure 33. Final biogas production chart.
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5. SUGGESTED READING: BMP PRODUCTION CURVES AND LIMITATIONS (INHIBITION/TOXICITY)
As well as an indicator of biogas potential, the test can provide information about potential sample
inhibition, or inoculum strength. The kinetics of biogas generation obtained through BMP test can provide
data on potential sample inhibition, toxicity or inoculum strength. Biodegradability characteristics of
substrates and production of inhibitory intermediate products will mainly control the kinetics of the
different steps of anaerobic digestion and define the shape of the biogas production curve.
Interpretation of the BMP assay results is of paramount importance. A valid concern exists regarding the
suitability of using the results of the BMP assay, a laboratory scale, batch test, to predict the performance
of semi- or continuous-flow, commercial size anaerobic digesters. In addition to the physical differences
in the fluid- and thermo-dynamic characteristics given by the reactor’s scale and geometry, batch reactors
and semi- or continuous-flow digesters essentially differ in their mode of operation. The way the reactor
is fed has a fundamental impact on the thermodynamic equilibrium of the anaerobic process – and thus,
on the food-web interactions. Semi- and continuous-flow digesters are characterized by dynamic changes
due to periodic substrate feeding and product removal – thus, unless the digester undergoes shock loads
or sudden environmental changes, process unbalance (and product accumulation) rarely occurs under
steady-state conditions. In contrast, in a batch reactor, unless removed via biologically-mediated
processes, substrates, microorganisms, enzymes, intermediate products, and (sometimes) final products
are accumulated within the system. When the concentration of an intermediate product (particularly,
volatile fatty acids and hydrogen) reaches the homeostatic threshold of a certain organism, or group of
organisms, the thermodynamic balance is altered, and one or several metabolic reactions may be
inhibited, causing further product accumulation and delay of substrate degradation. In most cases,
product inhibition is reversible, and as soon as thermodynamic conditions become favourable, reactions
resume.
Figure 34. BMP assay curves for a 40-day run showing four distinctive biogas production patterns (mL @ STP) from four different substrates; A: dairy manure, B: cheese whey, C: used vegetable oil, D: corn silage; error bars represent the standard deviation.
Reference: Labatut, 2012. Anaerobic Biodegradability of complex substrates: Performance and
Stability at Mesophilic and Thermophilic Conditions. Cornell University, 25- 28.
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The BMP assay is designed to provide ideal anaerobic conditions and prevent any form of biochemical
inhibition. To ensure this, three important conditions should be met throughout the BMP assay: 1)
appropriate microbial community, enzyme pool, and nutrients are present; 2) environmental conditions
are optimal; and 3) substrate and intermediate product concentrations are well below inhibitory/toxic
levels. Nevertheless, product inhibition is difficult to prevent, and indeed occurs in some BMP assays.
Fortunately, product inhibition primarily affects reaction kinetics, and thus, provided that adequate
digestion time is allowed, stabilization of the substrate’s biodegradable fraction and maximum
biomethane yields should be achieved. However, a more difficult problem to foresee, which directly
affects the biomethane potential, is trace element deficiency. This can occur during long-term anaerobic
digestion of certain substrates lacking an essential element, such as cobalt in thin stillage (Agler et al.,
2008). Accordingly, the BMP assay may not be a suitable test to predict biomethane yields, stabilization
performance, or possible process failure due to shock loads and product inhibition, over long-term semi-
and continuous-flow anaerobic digestion operations. BMP results should be limited to a relative
interpretation of the substrate’s biomethane potential, and not for an absolute estimation of daily
biomethane yields or the overall performance and stability of largescale digesters. The BMP assay is best
suited when used to elucidate what types of substrates, from an array of potential substrates, have the
highest biomethane 28 | P a g e potential. In addition, the assay can be used to estimate the potential
ideal ratios between co-substrates when co-digestion is intended. Lastly, BMP assay results can be used
to determine the extent of anaerobic biodegradability of substrates, and thus, relative residence times
required for complete digestion.
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FREQUENTLY QUESTIONS
1) What is the volume and material of the bioreactors?
We have standardised our reactors to 1 litre wide mouth HDPE bottles, allowing for larger samples and
inoculums to be processed, which further reduces potential error. HPDE is biological inert and remains
stable at 100°C.
2) What is the allowed (or suggested) minimal volume of digestate in 1L bioreactors?
We use 650-700 ml of inoculum + sample in the 1 litre reactor bottles. With this volume, the test ports
are below the liquid level and we can syringe out samples for analysis without having to lose biogas.
However, if you want to use smaller sample volumes you can do so using the same 1 litre bottles.
3) How many ports are available for sampling?
There is an access test tube provided on the reactor head which goes below the liquid level. This allows
you to syringe out sample for analysis and also to measure pH without losing biogas. The pH and redox
potential are not monitored continuously by our Arduino system. You can use a hand held pH meter with
6 mm pH probe to measure the pH. Apart from the test port and an in use biogas port, we have two
additional gas ports that can be used for flushing the reactor headspace. Any bespoke ports required will
incur additional charge.
4) How can gas samples be taken for subsequent GC analysis?
You can analyse the biogas composition using Tedlar gas bags attached at the outlet.
Our gas flow meters have individual chambers for each reactor. The gas from the bioreactors enters the
gas flow meter from the bottom and bubbles through the water to fill a vessel. As the vessel fills, it floats
then tumbles and this triggers the logging of the occurrence and the storage of the temperature and
pressure at each occurrence. After the tipping, the gas is evacuated to the headspace of the gas flow
meters. Each headspace has a hose tail fitting where a Tedlar gas bag of 5 litres or 10 litres can be fitted
to collect the biogas after measuring gas flow. The biogas composition collected in the gasbags can be
analysed using GC or a portable gas analyser.
The other way to do it is to fill the gas flow meter with caustic solution instead of water. The caustic
solution scrubs out the carbon dioxide as the gas enters the gas flow meter from the bottom and you will
be measuring methane flow instead of biogas flow. We recommend using the first method as it gives
flexibility to measure the Methane, Carbon dioxide, Hydrogen sulphide, Oxygen content.
5) How are the reactors mixed?
All reactors are mixed at exactly the same speed through stainless/silicone paddles driven by a gearbox.
One motor for 15 reactors. Stainless steel/silicone paddles deliver consistent mixing to all digesters in
each set. Most commercially-available BMP sets do not guarantee equal mixing for all reactors in the set.
Some rely on daily manual shaking, shaking surfaces, magnetic stirrers, etc., which is ok for absolute values
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of BMP but limits the use of kinetic data for rapid evaluation of inhibition or of the effect of feedstock
composition on dynamics of biogas production
If needed, the mixing can be controlled by a commercial timer to come on and off at the set timings.
6) How is the temperature controlled?
The temperature of operation is controlled by immersion of reactors in a Grants © water bath up to 95ºC
with 0.5º C setting resolution. A lid that holds the reactors in place has been designed to minimise the loss
of bath water by evaporation, facilitating tests at thermophilic temperatures without the common issues
of water evaporation when operating water baths at thermophilic temperature.
7) How is the data recorded?
The main data logging software is stored on the Arduino monitor which is integrated at the end of the gas
flow meter. There are three utilities which run on a laptop that is connected to the Arduino over USB.
These utilities are 'startrun' - which is used to transfer basic experimental data to the Arduino at
commencement of a run, 'filegrab' - which is used to transfer the log files built up by the Arduino back to
the laptop and 'monitor' - which provides a simple monitoring facility. Results are written to a number of
.csv log files which can be opened with Excel or similar. These files are held on a microSD card which is
part of the Arduino system and can be uploaded to the laptop at any time and as often as required (eg
daily) using the filegrab utility.
The gas flow meter automatically logs the final gas yield results in ml/day or ml/g VS and compensates to
standard temperature and pressure (STP) automatically in real time. The results can be obtained using
the 'Filegrab' utility on the laptop.
8) What is the minimal computer configuration to support the Arduino software?
A computer or laptop with Windows 10 with a spare USB port – can be a 32 bit machine or a 64 bit machine
– software supports both.
9) Could some assembly parts be bought separately if others do not fit our needs?
We do not sell our equipment in parts. The only thing we can sell separately is 15 cell gas flow meter.
10) Could some assembly parts be bought separately if others do not fit our needs?
Some user dose algaecide into the gas flow meters. Prepare a solution of bleach and fill the gas flow meter
with it leaving it soaking overnight. Then, shake the gas flow meter gently and flush connecting a water
hose at gentle rate for a few minutes. This will not leave the gas flow meter sparking clean, but it will be
clearer. If the film is firmly attached, then you might need to remove the top lid and with a bleach solution
brush the buckets. The ultimate wash would be to remove the tumbler buckets and give the machine a
thorough clean.
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6. ROUTINE CHECKS
a. Check the water level in the water bath. b. Check the water level in the gas flow meter and top up if the water is below the
spill point.
c. Check the tumbler buckets are not stuck in the vertical position (it could happen
if gas flow exceeds the tumbler capacity).
8. SPARES
The following spares can be purchased from Anaero Technology: reactor bottles, reactor bottle heads,
motors, water bath, hose, access port caps and seals.
Send an email to [email protected] or [email protected] or
[email protected] get a quote for any of the spares mentioned above.
REFERENCES
1. Walker, M. et al. (2010). “Residual biogas potential test”. Bioresource Technology. 100(24) 6339-6346. Available
at:
http://www.wrap.org.uk/sites/files/wrap/Residual%20Biogas%20Potential.pdf
2. Walker, M. et al. (2009). “Potential errors in the quantitative evaluation of biogas production in anaerobic digestion
processes”. Bioresource Technology. 100(24) 6339-6346. Available at:
http://www.sciencedirect.com/science/article/pii/S0960852409008876?via%3Dihub
3. Wrap (2013). “A review of the application of the Residual Biogas Potential (RBP) test for PAS110 as used across
the UK's Anaerobic Digestion industry, and a consideration of potential alternatives”. Available at:
http://www.biofertiliser.org.uk/images/upload/news_34_PAS110-digestate-stability-review.pdf
© Anaero Technology provides this manual strictly for reference use during operation of
equipment supplied to the client. The intellectual property on the design is not transferred or
licensed by provision of this manual and remains fully with Anaero Technology Ltd.
Unauthorised adaptation, or copying of the equipment will constitute an infringement of
intellectual property rights.